1. Field of the Invention
The invention relates to the field of systems for securing and transporting cargo external to an aircraft.
2. Description of Related Art
The cargo-carrying capability of aircraft is limited to cargo having overall external dimensions that are compatible with the dimensions of the aircraft cargo door(s), i.e., that can be loaded through the cargo door(s). Pragmatically, therefore, oversized cargo (external dimensions greater than the cargo door dimensions) or cargo having unusual external dimensions/configurations cannot be transported internally within the aircraft.
Various aerial transport systems are known that utilize an external securement system for transportation of larger loads. Helicopters, in particular, are often adapted for use in the transportation of large or bulky goods externally to the craft, such as timber, vehicles, and particularly large cargo containers. Typical underslung load hooks are capable of carrying external loads of at least 10,000 pounds.
One system for securing loads involves an underslung hook assembly, with a hook rigged to a pendent line, which is in turn attached to the aircraft external surface. U.S. Pat. No. 4,441,750, teaches a cargo sling system for suspension from an aircraft. The system includes a remotely actuable hook assembly and a guide that includes ring-like retainers through which sling lines pass after passage about the load.
U.S. Pat. No. 6,167,928, discloses a method of logging a tree utilizing a logging tool with a body having a connection for a lifting device using a hook. A guide extends vertically downwards away from the body when the tool is connected only to the lifting device. There is a hook on the body to one side of the guide for engaging an object. When the hook engages an object and the body is lifted by the lifting device, the body rotates and the guide rotates about the hinge so that the guide continues to extend vertically.
For safety concerns, the systems are typically provided with a system for releasing the load under controlled circumstances. U.S. Pat. No. 5,850,991, teaches a mechanical emergency dual-release mechanism for an external cargo hook system of an aircraft, where the hook assembly is operative to jettison an externally-attached cargo. The cabin pulley assembly is functionally interconnected to the cargo hook assembly and operative in response to a mechanical stimulus generated by means of the cockpit pulley assembly or the cabin pulley assembly to activate the cargo hook assembly to jettison the externally-attached cargo.
These and other related hook assemblies typically include a release that is actuable from the aircraft, which can be electric, manual, or both. An external cargo hook system allows oversized cargo or cargo having unusual external dimensions/configurations to be readily transported by the aircraft. While an external cargo hook system does enhance the versatility of the aircraft, it also poses some considerations that impact the overall design of the aircraft.
One disadvantage of the systems is that the components add both weight and drag to the aircraft. Drag is a particular problem for aircrafts that are capable of high speed flight, and the problem is magnified where the aircraft pendent guide lines and hooks are attached. Externally-attached cargo is typically suspended some distance below the aircraft such that the aircraft and its externally-attached cargo in effect define a pendent, or pendulum system, with the aircraft acting as the fixed support for the pendent. The weight and bulk of this system can reduce the speed and or add enough to the weight of the aircraft to decrease fuel efficiency.
The added weight is particularly problematic for aircraft systems that are only occasionally employed in the transport of cargo, yet are required to carry a cargo assembly at all times. In this situation, the assembly can add considerable weight, even when stowed on board the aircraft, and decrease the fuel efficiency of the aircraft in normal operation.
None of the prior approaches have been able to provide and external cargo system that addresses the requirements of aircraft systems that are capable both of flight at high speeds and still be rigged for carrying external loads.